Ruiz, U.S. Pat. No. 4,385,635, discloses an angiographic catheter having a soft flexible, pliable, leading tip zone, wherein the catheter is composed of a main reinforced length and an intermediate zone between the tip zone and the main length, the main length being reinforced by an inner tube of a polyamide material and wherein the polyamide is tapered in the intermediate zone to provide a tapered reinforced section tapering distally and uniformly to zero of the tip zone, so that the distal end is of elastomeric material, such as urethane, constituting a soft tip. Flynn, U.S. Pat. No. 4,282,876, discloses multiwall and co-tapered multiwall tubing constructions, wherein either the interior tubular portion or the concentric outer shell comprises a radiopaque composition. Burlis et al., U.S. Pat. No. 3,752,617, relates to the extrusion of tubing having different characteristics along its axial length. Flynn, U.S. Pat. No. 3,618,614, discloses multiwall surgical tubing comprising a relatively thick, transparent tube encased in a relatively thin, visually transparent outer shell. In a preferred embodiment, the thermoplastic material of said outer shell will be a denser, stiffer material than that of the core material to provide adequate torque resistance to the assembly and to provide the hard, slick exterior properties desired.
The prior art illustrates attempts to provide flexible catheter tubing with a soft tip and a stiff body, in order to provide the required degree of insertion and manipulation ease without producing patient trauma in the sensitive internal passageways. Rigidity is required to allow advancement of the catheter by pushing, to allow susceptibility to axial movements of adjustment and to resist twisting or torque forces. Such catheters must also be able to withstand a high bursting pressure.
For example, in constructing tubing for use in artificial kidney connections to the patient, it is desirable to have a tube with a stiff end and a flexible end. One method of constructing such tubing in the past has been to chemically remove the plasticizer from one end of the tube. Another method of making such a tube is to take two separate sections of different plastic tubes and fasten them together employing a suitable joining process. Neither of these methods have been completely satisfactory. The chemical removal of plasticizer results in inconsistent levels of flexibility in the end of the tube, and fastened tube sections possess the inherent risk of separation, causing internal injuries to the patient.
As shown above, some catheter tubing constructions found in the art have also attempted to increase resistance to torque by co-tapering different resins. While such a method may have the effect of providing enhanced torque resistance on one end of the tube, the torque resistance diminishes as the co-tapering progresses. As a result, co-tapering as a method to increase torque resistance, when used alone, is not sufficient to provide torque resistance throughout the entire non-tip length of the tubing. Thus, such tubing is not adequate for complicated applications where high torque resistance is required throughout the length of the tubing to provide ease of application through tortuous body passages.
The catheter tubing constructions found in the art also do not provide the combination of torque resistance and a soft tip, because the soft tip has generally inconsistent properties and is a solid, non-connected part of the tubing. For instance, neither Flynn, U.S. Pat. No. 4,282,876, nor Flynn, U.S. Pat. No. 3,618,614, provide a soft tip for the tubing.
Surprisingly, catheter tubing comprising a hard outer shell and a soft interior portion provides the resistance to torque required for insertion through tortuous body passages, without diminished flexibility or diminished frictional effect. Furthermore, such constructions, by utilizing soft interior portions, are more responsive to guide wire control than are hard interior portions. Additionally, constructions in which the soft interior portion extends beyond the hard outer shell obviates the need for attaching a soft tip to the tubing, thus avoiding the risk of separation of element. This is precisely the opposite approach than was taken by Ruiz, who emphasizes the desirability of having a soft outer shell.